With the increasing demands, particularly in the United States, for assurance of safety of automobiles and lightening of automobiles for energy saving, the conventionally employed metal bumpers have recently been replaced by urethane bumpers.
The leading materials for the currently used urethane bumpers are RIM urethanes. Bumpers made of RIM urethane are characterized by high impact resistance, excellent energy absorbing properties, light weight, satisfactory moldability, wide freedom of design, excellent coating properties, and the like.
On the other hand, RIM urethane-made bumpers are inferior in weather resistance, heat resistance, low-temperature resistance, and the like. Besides, RIM urethanes have productivity problems such that the molding cycle is long and the post-treatment takes much time and that scraps cannot be recycled, resulting in a great loss.
In recent years, thermoplastic olefinic elastomers (hereinafter referred to TPO) have been developed as soft bumper materials which eliminate the above-described disadvantages of RIM urethane-made bumpers. TPO molded articles have a superiority over the RIM urethane molded articles in terms of weight, weather resistance, heat resistance and low-temperature resistance. Further, TPO not only has good processability on injection molding but also incurs a minimized loss of molding because scraps in molding can be recycled.
However, TPO is inferior to RIM urethanes in terms of appearance of molded articles, particularly gloss and surface uniformity, and scratch resistance, and the application to be made of it is so limited. It has been, therefore, keenly demanded to solve these problems of appearance and physical properties of soft bumpers.